### What problem does this PR solve?

Add missing env var `MYSQL_MAX_PACKET` to service_conf.yaml.template,
and add default values to opendal config to fix npe.

### Type of change

- [x] Bug Fix (non-breaking change which fixes an issue)

### What problem does this PR solve?

Use `quote_plus` to escape password in opendal's mysql url to support
special characters like `#`.

### Type of change

- [x] Bug Fix (non-breaking change which fixes an issue)

### What problem does this PR solve?

Fix the config option name of the opendal table name and setting of
'max_allowed_packet'.

### Type of change

- [x] Bug Fix (non-breaking change which fixes an issue)

Signed-off-by: He Wang <wanghechn@qq.com>

**Context and Purpose:**

This PR automatically remediates a security vulnerability:
- **Description:** Detected possible formatted SQL query. Use
parameterized queries instead.
- **Rule ID:**
python.lang.security.audit.formatted-sql-query.formatted-sql-query
- **Severity:** HIGH
- **File:** rag/utils/opendal_conn.py
- **Lines Affected:** 98 - 98

This change is necessary to protect the application from potential
security risks associated with this vulnerability.

**Solution Implemented:**

The automated remediation process has applied the necessary changes to
the affected code in `rag/utils/opendal_conn.py` to resolve the
identified issue.

Please review the changes to ensure they are correct and integrate as
expected.

### What problem does this PR solve?

This PR fixes two issues in the OpenDAL storage connector:
1. The ‎`health` method was missing, which prevented health checks on
the storage backend.
3. The initialization of the ‎`opendal.Operator` object included a
redundant scheme parameter, causing unnecessary duplication and
potential confusion.

### Type of change

- [x] Bug Fix (non-breaking change which fixes an issue)

### Background
- The absence of a ‎`health` method made it difficult to verify the
availability and reliability of the storage service.
- Initializing ‎`opendal.Operator` with both ‎`self._scheme` and
unpacked ‎`**self._kwargs` could lead to errors or unexpected behavior
if the scheme was already included in the kwargs.

### What is changed and how it works?
- Adds a ‎`health` method that writes a test file to verify storage
availability.
- Removes the duplicate scheme parameter from the ‎`opendal.Operator`
initialization to ensure clarity and prevent conflicts.

before:
<img width="762" alt="企业微信截图_46be646f-2e99-4e5e-be67-b1483426e77c"
src="https://github.com/user-attachments/assets/acecbb8c-4810-457f-8342-6355148551ba"
/>
<img width="767" alt="image"
src="https://github.com/user-attachments/assets/147cd5a2-dde3-466b-a9c1-d1d4f0819e5d"
/>

after:
<img width="1123" alt="企业微信截图_09d62997-8908-4985-b89f-7a78b5da55ac"
src="https://github.com/user-attachments/assets/97dc88c9-0f4e-4d77-88b3-cd818e8da046"
/>

### What problem does this PR solve?

This PR resolves the inconsistency in the opendal configuration where
both ‎`schema` and ‎`scheme` were used as keys. The code and
configuration file now consistently use ‎`scheme`, which helps prevent
configuration errors and runtime issues. This change improves code
clarity and maintainability.

### Type of change

- [x] Bug Fix (non-breaking change which fixes an issue)

### Additional context
- Updated both ‎`conf/service_conf.yaml` and
‎`rag/utils/opendal_conn.py` to use ‎`scheme` instead of ‎`schema`
- No breaking changes to other configuration fields

### What problem does this PR solve?

#8074
Oss support opendal(including mysql)

### Type of change

- [x] New Feature (non-breaking change which adds functionality)

---------

Co-authored-by: Kevin Hu <kevinhu.sh@gmail.com>